1881.] 



MICKOSCOPICAL JOCENAL. 



31 



On Ossification and the Consti- 

 tution of tlie Dental System 

 of Balaenoptera Rostrata. 



The results of the researches of Mr. 

 C. Julin, conducted upon the foetus of 

 this animal, are given in full in the 

 Archives de Biologic as mentioned last 

 month, and occupy about fifty pages 

 of that periodical. The article is illus- 

 trated by two large and beautifully 

 colored plates. The general conclu- 

 sions are given as follows : — 



1. I have confirmed the existence 

 of follicles, or of gcrmcs dcntaircs, in 

 the inferior maxillary of the foetus of 

 Balcznoptera rostrata. 



2. In this maxillary, 84™™- in length 

 from the symphysis to the condyloid 

 extremity, there are forty-one follicles 

 lodged in the alveolar groove of the 

 symphysis at the coronoid process, 

 and disposed in a continuous series. 



3. These dental follicles present 

 the same constitution as those of all 

 other mammifers; their texture is pre- 

 cisely the same. 



4. The dental system of our Bala- 

 nopter only recalls that of the Ceto- 

 donts by the very considerable num- 

 ber of teeth ; if the system is based 

 upon the consideration of the form 

 of the organs, the Mysticetes are more 

 closely allied to the Pinnipedes and 

 especially to the Squalodons. 



5. Among the true Cetacea there 

 are none of which the dental system 

 can be compared with that of our 

 Balaenopter. All the Cetodonts (Del- 

 phinides and Ziphioides) are horao- 

 donts, and their teeth are all canini- 

 form, conical, and have a simple 

 root. Our Balaenopter is heterodont, 

 like the Pinnipedes and the Squalod- 

 ons, and its dental system corresponds 

 by its composition, to that of the 

 Squalodons; based upon the compara- 

 tive study of the dental system, the 

 Mysticetes, close neighbors of the 

 Squalodons should be considered like 

 the latter, as a transition type between 

 the Cetodonts and the Pinnipedes, to 

 which they are connected by the in- 

 termediate Zeuglodons. 



6. Meckel's cartilage intervenes in 

 the formation of the bony maxillary : 

 it gives origin to some bony channels 

 {travecs). 



7. These bony channels are made 

 continuous with the osseous channels 

 formed at the expense of other tissues 

 entering into the composition of the 

 bony maxillary, by the medium of a 

 deep osseous channel developed at 

 the expense of the perichondrium. 



8. In the beginning, the single in- 

 tra-osseous portion of Meckel's cartil- 

 age suffers modifications in its struc- 

 ture, the extra osseous part remains 

 constituted like hyaline cartilage. 



9. The ossification of Meckel's 

 cartilage takes place in a manner 

 analogous to that of the cartilaginous 

 nucleus of the diaphyse in the ossifi- 

 cation of a long bone. 



10. The condyle is formed by a 

 cartilaginous nucleus which becomes 

 ossified. 



11. The coronoide apophyse is not 

 composed of cartilage, as in man. 



12. The formation of medullary 

 spaces in a cartilaginous nucleus 

 (Meckel's cartilage or condyle) during 

 ossification is due to modifications 

 which the fundamental substance of 

 the cartilage may undergo; it may be 

 either calcified, impregnated with bony 

 substance, or even hypertrophied 

 (condyle). 



13. The young medullary tissue, 

 either when the ossification of the 

 cartilage or of the conjunctive tissue 

 proper is concerned, is the result of 

 modifications undergone by the oste- 

 ogenous tissue. Its texture is the 

 same as in the other case. 



14. The osteoblasts form at the ex- 

 pense of the elements of the young 

 medullary tissue. 



15. The beginning of the ossifica- 

 tion of one or the other of the tissues 

 constituting the inferior maxillary, 

 corresponds to what is understood by 

 "direct or metaplasmic ossification." 



16. There is complete analogy be- 

 tween the ossification of cartilage and 

 that of conjunctive tissue, properly 

 so-called. 



